Cacheable key on multiple method arguments

Question

From the spring documentation     Cacheable value  bookCache   key  isbn   public Book findBook ISBN isbn  boolean checkWarehouse  boolean includeUsed    How can I specify  Cachable to use isbn and checkWarehouse as key

User · Answer

This will work     Cacheable value  bookCache   key   checkwarehouse toString   append  isbn toString

User · Answer

After some limited testing with Spring 3 2  it seems one can use a SpEL list                   This can also include null values  Spring passes the list as the key to the actual cache implementation  When using Ehcache  such will at some point invoke List hashCode    which takes all its items into account   I am not sure if Ehcache only relies on the hash code    I use this for a shared cache  in which I include the method name in the key as well  which the Spring default key generator does not include  This way I can easily wipe the  single  cache  without  too much     risking matching keys for different methods  Like    Cacheable value  bookCache      key     root methodName   isbn  id   checkWarehouse     public Book findBook ISBN isbn  boolean checkWarehouse         Cacheable value  bookCache      key     root methodName   asin   checkWarehouse     public Book findBookByAmazonId String asin  boolean checkWarehouse        Of course  if many methods need this and you re always using all parameters for your key  then one can also define a custom key generator that includes the class and method name    lt cache annotation-driven mode       key-generator  cacheKeyGenerator    gt   lt bean id  cacheKeyGenerator  class  net example cache CacheKeyGenerator    gt       with   public class CacheKeyGenerator    implements org springframework cache interceptor KeyGenerator         Override     public Object generate final Object target  final Method method         final Object    params             final List lt Object gt  key   new ArrayList lt  gt             key add method getDeclaringClass   getName             key add method getName              for  final Object o   params                key add o                     return key

User · Answer

You can use Spring SimpleKey class   Cacheable value    bookCache   key    new org springframework cache interceptor SimpleKey  isbn   checkWarehouse

User · Answer

You can use a Spring-EL expression  for eg on JDK 1 7    Cacheable value  bookCache   key  T java util Objects  hash  p0  p1   p2

User · Answer

Use this   Cacheable value  bookCache   key   isbn          checkWarehouse          includeUsed

User · Answer

Update  Current Spring cache implementation uses all method parameters as the cache key if not specified otherwise  If you want to use selected keys  refer to Arjan s answer which uses SpEL list   isbn   includeUsed   which is the simplest way to create unique keys  From Spring Documentation  The default key generation strategy changed with the release of Spring 4 0  Earlier versions of Spring used a key generation strategy that  for multiple key parameters  only considered the hashCode   of parameters and not equals    this could cause unexpected key collisions  see SPR-10237 for background   The new  SimpleKeyGenerator  uses a compound key for such scenarios   Before Spring 4 0 I suggest you to concat the values of the parameters in Spel expression with something like key  quot  checkWarehouse toString      isbn toString   quot    I believe this should work as org springframework cache interceptor ExpressionEvaluator returns Object  which is later used as the key so you don t have to provide an int in your SPEL expression  As for the hash code with a high collision probability - you can t use it as the key  Someone in this thread has suggested to use T java util Objects  hash  p0  p1   p2  but it WILL NOT WORK and this approach is easy to break  for example I ve used the data from SPR-9377       System out println  Objects hash  quot someisbn quot   new Integer 109   new Integer 434         System out println  Objects hash  quot someisbn quot   new Integer 110   new Integer 403      Both lines print -636517714 on my environment  P S  Actually in the reference documentation we have  Cacheable value  quot books quot   key  quot T someType  hash  isbn  quot    public Book findBook ISBN isbn  boolean checkWarehouse  boolean includeUsed   I think that this example is WRONG and misleading and should be removed from the documentation  as the keys should be unique  P P S  also see https   jira springsource org browse SPR-9036 for some interesting ideas regarding the default key generation  I d like to add for the sake of correctness and as an entertaining mathematical computer science fact that unlike built-in hash  using a secure cryptographic hash function like MD5 or SHA256  due to the properties of such function IS absolutely possible for this task  but to compute it every time may be too expensive  checkout for example Dan Boneh cryptography course to learn more

[java] @Cacheable key on multiple method arguments

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